Fungible bitumen from paraffinic centrifugation

ABSTRACT

A process for cleaning bitumen froth produced from an oil sands extraction process involves mixing a sufficient amount of paraffinic solvent with the bitumen froth; subjecting the resulting mixture to centrifugal separation in a centrifuge to yield a diluted bitumen product, a water byproduct stream, and a solids byproduct stream; and processing the diluted bitumen product to yield dry fungible bitumen product having a total water/solids content less than about 0.5 wt %, and a recyclable paraffinic diluent stream.

FIELD OF THE INVENTION

The present invention relates generally to a paraffinic bitumen froth treatment process using centrifugation to produce a fungible bitumen product.

BACKGROUND OF THE INVENTION

Oil sand generally comprises water-wet sand grains held together by a matrix of viscous heavy oil or bitumen. Bitumen is a complex and viscous mixture of large or heavy hydrocarbon molecules which contain a significant amount of sulfur, nitrogen and oxygen. Oil sands processing involves extraction and froth treatment to produce diluted bitumen which is further processed to produce synthetic crude oil and other valuable commodities. Extraction is typically conducted by mixing the oil sand in hot water and aerating the resultant slurry to promote the attachment of bitumen to air bubbles, creating a lower-density bitumen froth which floats and can be recovered in a separator such as a gravity separator or cyclonic separator. Bitumen froth may contain about 60 wt % bitumen, about 30 wt % water and about 10 wt % solid mineral material, of which a large proportion is fine mineral material. The bitumen which is present in a bitumen froth comprises both non-asphaltenic material and asphaltenes.

Froth treatment is the process of significantly reducing the aqueous and solid contaminants from the bitumen froth to produce a clean diluted bitumen product (i.e., “diluted bitumen” or “dilbit”) which can be further processed to produce a fungible bitumen product that can be sold or processed in downstream upgrading units. It has been conventional to dilute this bitumen froth with a hydrocarbon solvent to reduce the viscosity and density of the oil phase, thereby accelerating the settling of the dispersed phase impurities by gravity or centrifugation. This diluted bitumen froth is commonly referred to as “dilfroth.” It is desirable to “clean” dilfroth, as both the water and solids pose fouling, corrosion and erosion problems in upgrading refineries.

Either a paraffinic or naphthenic type diluent may be used. The difference in the bitumen produced by use of either a paraffinic or naphthenic type diluent can be attributed largely to the presence of aromatics in naphthenic-type diluents. Aromatics have the ability to hold asphaltenes in solution, whereas paraffinic type diluents cause asphaltene precipitation. The use of naphthenic type diluents results in a relatively high bitumen recovery (generally greater than about 98%), but in a diluted bitumen product which has relatively high water (about 2 to 4 wt %) and solids (about 0.5 to 1.0 wt %) concentrations. The combined water and solids concentration typically is greater than about 2.5 wt %. Due to the level of contamination, which pose fouling, corrosion and erosion problems, the diluted bitumen is not suitabie for direct pipelining to conventional refineries, cannot be sold to the open market, and must be upgraded using processes such as a coker or hydroprocessing. The upgraded products are then hydrotreated to produce synthetic crude oil.

Use of paraffinic type diluents results in a relatively lower overall bitumen recovery (generally about 90%), but in a bitumen product which is dry, light, and has a relatively low total water and solids concentration (less than about 0.5 wt %). However, paraffinic type diluents precipitate a major proportion of asphaltenes from the bitumen froth, resulting in not only the trapping of water and solids by the asphaltenes, but also high asphaltenic hydrocarbon losses (about 8%) to froth treatment tailings. There are both environmental incentives and economic incentives for recovering all or a portion of this residual asphaltenic hydrocarbon.

To separate the bitumen from water and solids, naphtha-treated bitumen froth is commonly subjected to 1 g gravity separation in inclined plate separators in series with high g centrifugation. Paraffinic-treated bitumen froth is typically subjected to phase separation and 1 g gravity separation, with sufficient space needed to accommodate large gravity separation vessels.

However, treatment processes using a naphthenic type diluent may still result in bitumen often containing undesirable amounts of solids and water. Product solids lead to increased wear of downstream equipment, higher maintenance costs, and unplanned capacity losses and outages. In addition, hydrocarbon may also be lost to tailings due to inefficient separation. Recovery of the solvent from the diluted bitumen product is required before the dry fungible bitumen may be delivered to a refinery for further processing.

Solvent and precipitated asphaltenes may also be lost to the tailings. Since the rejected asphaltenes (7-8 wt % of the original bitumen in froth) can be used as fuel or feedstock for various applications, the disposal of asphaltenes in the tailings pond is wasteful. Recovery of solvent is desirable to avoid discarding flammable, carcinogenic solvent in a tailings pond and to minimize expenditures for fresh solvent.

Accordingly, there is a need for a method of improving the quality of diluted bitumen product in bitumen froth treatment processes.

SUMMARY OF THE INVENTION

The present invention relates generally to a paraffinic bitumen froth treatment process using a decanter centrifuge to produce a fungible bitumen product. It was surprisingly discovered that by using the process of the present invention, one or more of the following benefits may be realized:

(1) The paraffinic bitumen froth treatment process of the present invention uses a decanter centrifuge to produce a fungible bitumen product amenable to downstream upgrading processes. Since a decanter centrifuge is used rather than multiple large gravity separation vessels, plot space requirements are reduced by about 70% and capital costs by about 50%.

(2) The hydrocarbon and fine solids loading on the tailings pond from froth treatment is reduced since the decanter centrifuge solids by-product stream can be further processed in a flotation cell to recover asphaltenic hydrocarbon and fine solids.

(3) Precipitated asphaltenes in the form of a dry granulated powder are recovered and recycled at particular steps within the process for use as feedstock or fuel for various applications rather than being lost to tailings. This processable asphaltene by-product may yield a saleable hydrocarbon liquid stream at a yield of about 40%.

(4) By recovering this asphaltenic hydrocarbon, diluent losses are reduced by about 20%. Recovery and recycling of paraffinic solvent at multiple steps within the process minimizes expenditures for fresh solvent makeup and reduces the losses of flammable, carcinogenic solvent in a tailings pond.

Thus, broadly stated, in one aspect of the present invention, a process for cleaning bitumen froth produced from an oil sands extraction process is provided, comprising:

-   -   mixing a sufficient amount of paraffinic solvent with the         bitumen froth;     -   subjecting the resulting mixture to centrifugal separation in a         centrifuge to yield a diluted bitumen product, a water byproduct         stream, and a solids byproduct stream; and     -   processing the diluted bitumen product to yield dry fungible         bitumen product having a total water/solids content less than         about 0.5 wt %, and a recyclable paraffinic diluent stream.

In one embodiment, the ratio of paraffinic solvent to raw froth by weight percentage ranges from about 0.5 to about 4.5.

In one embodiment, the centrifuge is a decanter centrifuge. In one embodiment, the decanter centrifuge is operated to generate a g-force ranging from about 1000 to about 5000.

In one embodiment, the process further comprises processing the water byproduct stream to recover residual bitumen and paraffinic solvent.

In one embodiment, the process further comprises processing the solids by-product stream to prepare a dry granulated powder comprising asphaltenes and fine solids.

For the purposes of the present invention, the term “fungible bitumen” is defined as a bitumen product wherein the sum of water and solids content is less than about 05 vol % to allow the hydrocarbon product to be able to be shipped down a pipeline to a conventional refinery.

The term “high g” decanter centrifuge is defined as a decanter centrifuge which is operated to generate a g-force ranging from about 1000 to about 5000.

Additional aspects and advantages of the present invention will be apparent in view of the description, which follows. It should be understood, however, that the detailed description and the specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will now be described by way of an exemplary embodiment with reference to the accompanying simplified, diagrammatic, not-to-scale drawing:

FIG. 1 is a schematic process flow diagram of an embodiment of the present invention for froth treatment.

FIG. 2 is a graph showing the product composition (volume (ml) of heavy phase, light phase, and solids) as a function of spin time (min at 1500 RPM).

FIG. 3 is a graph showing the product composition (volume (ml) of heavy phase, light phase, and solids) as a function of spin time (min at 1500 RPM) for two-phase (dashed line) and three-phase (solid line) decanter centrifuges.

FIG. 4 is a graph showing the water concentration (wt %) in the product light phase as a function of spin time (min at 1500 RPM).

FIGS. 5A-D are photographs of centrifuged paraffinic solids with diluent to bitumen (D/B, by wt %) ratios ranging from about 1.8 to about 4.5 un-kneaded (left panel) and kneaded (right panel).

FIG. 6 is a photograph of kneaded naphthenic cake from a decanter centrifuge.

FIG. 7 is a graph showing the water+solids content in diluted bitumen (wt %) as a function of solvent to bitumen ratio (wt/wt) when using either paraffinic solvent (octane) versus naphthenic solvent (naphtha).

FIG. 8 is a graph showing the water content in diluted bitumen (wt %) when using a mixed solvent (naphtha and octane) at various solvent/bitumen (wt/wt) ratios.

FIG. 9 is one configuration (Configuration #1) of the present invention where naphthenic froth treatment and paraffinic froth treatment are combined.

FIG. 10 is another configuration (Configuration #2) of the present invention where naphthenic froth treatment and paraffinic froth treatment are combined.

FIG. 11 is a graph showing the water in diluted bitumen content (wt %) when using either Configuration #1 (FIG. 9) or Configuration #2 (FIG. 10) of combined naphtha and paraffinic froth treatment.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

The detailed description set forth below in connection with the appended drawing is intended as a description of various embodiments of the present invention and is not intended to represent the only embodiments contemplated by the inventor. The detailed description includes specific details for the purpose of providing a comprehensive understanding of the present invention. However, it will be apparent to those skilled in the art that the present invention may be practised without these specific details.

The present invention relates generally to a paraffinic bitumen froth treatment process using a high g decanter centrifuge to produce a fungible bitumen product amenable to downstream upgrading processes. To meet specification requirements, the fungible bitumen product must have a total water and solids concentration of less than about 0.5 vol %.

FIG. 1 is a general schematic of a centrifuge-based froth treatment process using centrifuges, which can be used in one embodiment of the present invention. As used herein, the term “centrifuge-based” process refers to an operation in which bitumen is separated from water and solids using centrifugal acceleration resulting from rotational movement of a suitable apparatus. In one embodiment of the present invention, the apparatus is a decanter centrifuge. The process generally includes three pathways yielding one fungible bitumen product and two byproducts (contaminated water stream and concentrated solids stream).

In the process of the invention shown in FIG. 1, raw froth 10 is used as the feed. Raw froth 10 is initially received from an extraction facility which extracts bitumen from oil sand using a water extraction process known in the art. The raw froth 10, as received, typically comprises about 60% bitumen, about 30% water and about 10% solids, and thus, needs to be further cleaned prior to upgrading. The raw froth 10 is pumped via froth pump 12 into line 14. Generally, bitumen froth is deaerated in deaeration devices known in the art prior to pumping.

A diluent 16 is introduced via pump 18 into the in-line flow of raw froth 10. As used herein, the term “in-line” flow means a flow contained within a continuous fluid transportation line such as a pipe or other fluid transport structure which preferably has an enclosed tubular construction. In one embodiment, the diluent 16 is a paraffinic solvent. As used herein, the term “paraffinic solvent” (also known as aliphatic) means solvents containing normal paraffins, isoparaffins and blends thereof in amounts greater than 50 wt %. Presence of other components such as olefins, aromatics or naphthenes counteract the function of the paraffinic solvent and hence should not be present more than 1 to 20 wt % combined and preferably, no more than 3 wt % is present. The paraffinic solvent may be a C4 to C20 paraffinic hydrocarbon solvent or any combination of iso and normal components thereof. In one embodiment, the ratio of paraffinic solvent to raw froth (by wt %) ranges from about 0.5 to about 4.5.

Optionally, asphaltenes 20 in particulate form (i.e., asphaltene scavenger seed) may also be introduced via pump 22 into the in-line flow of raw froth 10 following addition of the diluent 16. As used herein, the term “asphaltenes” means hydrocarbons, which are the n-heptane insoluble, toluene soluble component of a carbonaceous material such as crude oil, bitumen or coal. Generally, asphaltenes have a density of from about 0.8 grams per cubic centimeter (g/cc) to about 1.2 g/cc. Asphaltenes are primarily comprised of carbon, hydrogen, nitrogen, oxygen, and sulfur as well as trace vanadium and nickel. The carbon to hydrogen ratio is approximately 1:1.2, depending on the source.

The mixture of raw froth 10, diluent 16, and/or asphaltenes 20 may then bypass or optionally, pass through a contactor 24 before being subjected to centrifugal separation. Mixing is conducted for a sufficient duration in order to allow the raw froth 10, diluent 16, and/or asphaltenes 20 to combine properly. Mixer settlers or columns are commonplace in the art and are exemplified by apparatuses including, but not limited to, stirred liquid-liquid extraction columns such as, for example, rotating disc contactors and the like. In one embodiment, the rotating disc contactor 24 is a mechanically agitated column which separates components of a mixture by adding to the mixture a suitable liquid solvent which dissolves or dilutes one or more components of the mixture, thereby facilitating their separation.

The mixture of raw froth 10, diluent 16, and/or asphaltenes 20 is subjected to centrifugal separation to yield a product stream comprising a diluted bitumen product 26 in line 36; and two by-product streams, one comprising a separate water by-product stream contaminated with trace diluent and hydrocarbon 28 in line 58; and the other comprising a solids by-product stream 30 (sands, clays, asphaltenes) in line 80. In one embodiment, centrifugal separation is conducted using a three-phrase decanter centrifuge 32.

The operation of three-phase decanter centrifuges is commonly known to those skilled in the art and will not be discussed in detail. Briefly, the three-phase decanter centrifuge 32 separates solids and two liquid streams from a mixture thereof. The three-phase decanter centrifuge 32 comprises an elongated bowl mounted for rotation along its longitudinal axis. A helical screw conveyor is coaxially mounted within the bowl. A back drive features a direct drive gearbox for automatically controlling the differential speed between the bowl and the conveyor in order to maintain a balance between liquid clarity and solids dryness, irrespective of variations in the feed mixture. Since the bowl and conveyor are caused to rotate at controlled different, speeds, solids sedimented against the bowl wall are conveyed along the inner annular surface thereof to solids discharge openings provided at the tapered end of the bowl. The clarified liquid from which the solids have been removed is decanted into a chamber where two liquid phases with different specific gravities (e.g., a heavy liquid phase, a light liquid phase) may be separated. The liquids are separated in the liquid zone and decanted through separate discharge systems to prevent cross-contamination. In one embodiment, the three-phase decanter centrifuge 32 is operated to generate a g-force ranging from about 1000 to about 5000.

The product stream comprises the diluted bitumen product 26 which contains bitumen, diluent, and trace amounts of residual water and solids (possibly less than about 0.5 wt % total). The diluted bitumen product 26 is transferred from the decanter centrifuge 32 to a diluent recovery unit (“DRU”) 34 via line 36. Diluent 38 is recovered from the DRU 34 via line 40, and transferred to line 42 where it can be combined with make-up diluent 43 and/or diluent 16.

The bitumen product (“dry bitumen”) 44 substantially free of water and mineral matter is recovered from the DRU 34 via line 46. As used herein, the term “dry bitumen” refers to dry or fungible bitumen having a solids content less than about 0.5 wt %. The dry bitumen 44 is transferred to either a storage unit 48 to be stockpiled for future use, a unit 49 for direct sale, or a fluid coker or ebullating-bed hydrocracker (“LC-Finer”) 50 for further processing into a synthetic crude oil product by means not shown but disclosed in the art. In general, fluid cokers upgrade heavy hydrocarbons to lighter products by removing carbon by thermal cracking. LC-Finers upgrade hydrocarbons in an ebullating catalyst bed by adding hydrogen in a hydroprocessing reaction. Virgin light gas oil (“LGO”) 52 is recovered from the DRU 34 via line 54, and further processed in downstream hydroprocessing units 56.

The water by-product stream 28 comprises water, and residual hydrocarbon, diluent, and fine solids. The water stream 28 exits the decanter centrifuge 32 through line 58 and may then bypass or optionally, pass through a high speed disc stack centrifuge 60 before being subjected to a final clean-up in a solvent recovery unit (“SRU”) 62. The disc stack centrifuge 60 may be used in the event that the water stream 28 contains a significant amount of bitumen, light hydrocarbon, and solids.

The operation of disk stack centrifuges is commonly known to those skilled in the art and will not be discussed in detail. Briefly, the disc stack centrifuge 60 separates bitumen from water and solids using extremely high centrifugal forces. When the heavy phase (i.e., water and solids) is subjected to such forces, the water and solids are forced outwards against the periphery of the rotating centrifuge bowl, while the lighter phases (i.e., hydrocarbon) forms concentric inner layers within the bowl. Plates (i.e., the disc stack) provide additional surface settling area, which contributes to speeding up separation. The bitumen and diluent 64 is transferred from the disc stack centrifuge 60 to the DRU 34 via line 66 for separation and processing as previously described.

The water and residual diluent having residual hydrocarbon contaminants (nozzle plus heavy phase water) 68 is transferred from the disc stack centrifuge 60 to the SRU 62 via line 70. The SRU 62 separates the residual diluent from the water and fine solids by steam stripping to produce a diluent stream 72 which may be combined with diluent 16 prior to addition to the froth feed 10 in line 14. The SRU 62 also produces a water and fine solids stream 74 which is disposed via pump 76 to a tailings pond 78.

The solids stream 30 comprises asphaltenes, coarse and fine solids, residual diluent, and hydrocarbon. The solids stream 30 is slurried with hot water upon exiting the decanter centrifuge 32 through line 80 and enters a flotation cell 82 for separation of an overflow hydrocarbon rich with fine solids stream 84 and an underflow stream of clean coarse solids 86. The hydrocarbon rich with fine solids stream 84 is treated with diluent 88 in line 90 before being further combined in a mixer 92 and transferred to a spray drier 94 which uses nitrogen 96 as the hot gas for drying. Within the spray drier 94, the asphaltene-diluent mixture is pumped through high delta P atomizing nozzles to form a spray pattern of fine droplets. As these droplets form, any diluent is flashed off, leaving behind asphaltenes and fine solids in the form of dry granulated powdered solids 98 at the bottom of the spray drier 94. The solids 98 may be transferred to a storage unit 100 to be stockpiled for various future uses.

In one embodiment, the solids 98 may be combined with diluent 110 prior to addition to the froth feed 10 in line 14 (i.e., as asphaltene scavenger seed 20). The diluent 110 can be a combination of water with paraffinic or aromatic diluent.

In one embodiment, the solids 98 may be combined with bitumen 112 in a mixer 114, heated in a heater 116, and thermally upgraded in a fluid bed or delayed coker 118.

In one embodiment, the solids 98 may be injected into a fluidized bed gasifier or fluid bed boiler 120 which converts the solids 98 into a syngas which can be further processed to produce a synthetic natural gas or to produce liquid fuels.

In one embodiment, the solids 98 may be used as fuel for utility boilers which convert water into steam for electricity generation and process applications.

In one embodiment, the solids 98 may be directed to a land storage facility 122 to be stockpiled for future use as an energy supply.

The flashed overhead vapour comprising diluent and water 124 is condensed in an overhead exchanger system comprising an OVH condenser 126 and decanter 128 to separate the diluent 130 from the water 132. The diluent 130 is transferred via pump 134 into line 136 which connects with line 42 going to the diluent storage tank 16. The diluent 130 may be combined with diluent 72 from the SRU 62 prior to routing to the diluent storage tank 16. The water 132 may bypass or optionally, be pumped via pump 138 to pass through the SRU 62 for recovery of any residual diluent before disposal in the tailings pond 78.

EXAMPLE 1

Experiments were conducted to investigate the ability of a three-phase decanter centrifuge to separate a light phase product having a water content below about 2.0 wt % from naphthenic diluted froth. To mimic separation in a decanter centrifuge, a benchtop Hotspin™ centrifuge was run at particular speeds and spin times. Samples of naphthenic diluted froth contained bitumen (44 wt %), naphtha (26 wt %), water (22 wt %), and solids (8 wt %), with the N:B ratio being about 0.6. The samples were maintained at 80° C. and spun at 1500 rpm for 1, 2, 4, and 8 mins. Two samples were prepared for each spin time. The reported values are the average values between the two samples at each spin time.

Three distinguishable interfaces between light phase, heavy phase and solids were achieved in each sample after each centrifugation interval. The separated heavy phase became less turbid when spun longer, while the overall combined volume of heavy phase and solids remained relatively constant. FIG. 2 shows the volumes of each of the three phases in the samples. The volume of the light phase remained relatively constant with increasing spin times. For each spin time the volume of light phase was about 77% of the total volume. In contrast, the volume of solids increased with longer spin times up to 4 min, after which the samples stabilized. Increasing the residence time appeared to aid in clarifying the heavy phase since its turbidity decreased with spin time The fact that the light phase volume remained constant with spin time is of interest when comparing the operation of a two-phase decanter to that of a three-phase decanter. A two-phase decanter separates only the solids from the liquid phase, meaning that the product is a combination of the light phase and heavy phase. In contrast, a three-phase decanter separates all three phases independently.

FIG. 3 shows the product composition (volume (ml) of heavy phase, light phase, and solids) as a function of spin time (min at 1500 RPM) expected using two-phase (dashed line) and three-phase (solid line) decanter centrifuges. Given that the residence time in a centrifuge is a function of feed rate, the product from the two-phase decanter centrifuge has a higher solids and water content at higher feed rates. In contrast, the product from the three-phase decanter centrifuge is independent of feed rate, implying that the three-phase decanter centrifuge may produce a more consistent product over a wider feed rate envelope compared to a two-phase decanter centrifuge.

The amount of water present in the separated light phase was measured using Karl Fisher titration. The water content (wt %) in the light phase after the tested spin times (min at 1500 RPM) is shown in FIG. 4. While the bulk of the light phase separated immediately, the water content continued to decrease with increasing spin times. The water concentration in the light phase was below the standard froth treatment water specification of about 2.0 wt % after only one minute of spin time. In comparison, the water content for a two-phase decanter is substantially higher since the heavy phase (water) is not separated from the light phase.

With use of a three-phase decanter centrifuge, the light phase of the troth separated from the heavy phase and solids relatively quickly, while the solids separated from the heavy phase over a longer time frame. After initial separation, the water content of the light phase was less than about 2.0 wt %. Volumetrically, a significant amount of the solids were removed from the light phase. Based on these results, a three-phase decanter centrifuge is suitable for producing a light phase which meets froth treatment product specifications of less than about 2.0 wt % water.

EXAMPLE 2

An experiment was conducted to assess the feasibility of a three-phase decanter centrifuge to convey separated solids in a paraffinic diluted froth treatment process. Pentane (C₅H₁₂) and undiluted froth were mixed in diluent to bitumen (D/B) ratios of about 1.8, 2.8, 3.5, and 4.5 by weight. These samples were poured into 8 oz jars and cold spun (room temperature) for 20 minutes at about 2,000 RPM. After spinning in the centrifuge, the liquid phase was poured out leaving only the solids. FIGS. 5A-D show these solids at the various DIB ratios before and after kneading with a lab spoon to simulate conveyance in a decanter centrifuge. For comparison, kneaded naphthenic cake is shown in FIG. 6. For each solid, the relative cohesive property, adhesion to the beaker and lab spoon, and shear strength were inspected.

It was expected that separating paraffinic solids trapped in viscous medium might be challenging in a decanter centrifuge. However, it was observed that the paraffinic solids became more brittle and lost their cohesive or gummy texture with increasing D/B ratios (FIGS. 5A-D) in comparison to the naphthenic solids which were more cohesive and gummy (FIG. 6). These preliminary observations indicate suitability of a paraffinic solvent to froth ratio in the range of about 1.8 to about 4.5 by weight, and that the conveyability of the paraffinic solids may be comparable to the conveyability of the naphthenic solids processed by decanter centrifuges in froth treatment.

EXAMPLE 3

Experiments were conducted to compare naphthenic treatment of bitumen froth at various solvent-to-bitumen ratios and paraffinic (octane) treatment of bitumen froth at various solvent-to-bitumen ratios using centrifugation. Each of the naphtha and octane solvents and bitumen froth were first heated inside a hot water bath at 80° C. To mimic separation in a decanter centrifuge, a benchtop Hotspin™ centrifuge was used. Two sets of experiments were performed for each of naphtha as solvent and octane as solvent. In Test 1 for naphtha, solvent-to-bitumen (S/B) ratios (wt/wt) of 0.5, 0.7, 1.0 and 2.0 were tested. In Test 1 for octane, solvent-to-bitumen (S/B) ratios (wt/wt) of 0.5, 1.0, 2.0 and 4.0 were tested. In Test 2 for naphtha, higher solvent-to-bitumen (S/B) ratios (wt/wt) of 2.0, 3.0, 3.5, 4.0, 4.5 and 5.5 were tested. In Test 2 for octane, solvent-to-bitumen (S/B) ratios (wt/wt) of 1.0, 1.2, 1.4, 1.5, 1.6, 1.8 and 2.0 and 4.0 were tested. Froth mixtures at each solvent ratio were mixed inside a hot water bath at 1000 rpm for 5 minutes. Froth samples (10 ml) were collected at each S/B ratios for each solvent and subjected to hot-spin centrifugation at 80° C. and 1400 rpm for 6 minutes. The top ˜4 ml of the diluted bitumen layer from the centrifuge tubes were drawn from each sample and analyzed using Karl Fischer analysis. Karl Fischer is an analytical test that measures the water content within the diluted bitumen samples. Solids were measured by diluting the recovered hydrocarbon product with toluene and filtering through a 1.6 micron pore size filter 55 mm in diameter. Recovered solids are then washed with excess toluene, the filter dried and weighed for comparison to the original mass of hydrocarbon filtered.

FIG. 7 is a plot of the water+solids content in diluted bitumen (wt %) for each of the S/B (wt/wt) ratios tested. It can be seen in FIG. 7 that when naphtha is used as the solvent, even at very high S/B ratios, e.g., 5.5, the amount of water+solids in the diluted bitumen was still fairly high, e.g., 0.9 wt %. However, when octane was used, the comparable amount of water+solids, e.g., 0.9 wt %, was obtained at a significantly lower S/B ratio, e.g., about 1.5. Furthermore, a fungible bitumen product could be produced at much lower S/B ratios when using octane. For example, at S/B (octane to bitumen) ratios of about 1.8 to about 2.0, the water+solids content in the diluted bitumen was reduced to about less than 0.2 wt %. However, an increase in S/B ratio from 2.0 to 4.0, when using octane, did not result in a further decrease in the wt % of solids+water.

In conventional bitumen froth treatment using naphtha, a S/B ratio (naphtha to bitumen) of 0.7 is used. Such a ratio (i.e., N/B ratio of 0.7) generally results in a diluted bitumen product having a total water+solids content of about 3.1 wt %. However, this diluted bitumen product is not considered to be fungible bitumen and must therefore be further treated. However, when using naphtha, bitumen recovery is very good, as the hydrocarbon loss when using a N/B ratio of 0.7 is only about 2%. On the other hand, the use of paraffinic solvent as shown in the present invention at a S/B ratio of 1.8 generally results in a diluted bitumen product having a total water+solids content of about 0.1 wt %, which is considered to be a fungible bitumen product. However, with paraffin, the trade-off is that bitumen recovery is lower, as the hydrocarbon loss is around 10%.

Thus, in one aspect of the present invention, paraffinic centrifugation can be used in conjunction with a conventional naphtha bitumen froth treatment plant which also uses centrifugation to obtain a fungible bitumen product having a water+solids content of about 0.5 wt % by blending products obtained from both naphtha froth treatment and paraffinic froth treatment of the present invention. By way of example, when using the highlighted values in FIG. 7, i.e., N/B ratio of 07 and O/S ratio of 1.8, to achieve 0.5 wt % water+solids in bitumen (i.e., fungible bitumen), one can blend 76.5% of the product from paraffinic (e.g., octane) centrifugation with 23.5% of the product from naphthenic centrifugation. Thus, by combining naphthenic centrifugation with paraffinic centrifugation, a fungible product can be produced. Furthermore, the hydrocarbon losses will be less than when using paraffinic centrifugation alone, as there will be an increase in hydrocarbons from 90% (paraffinic centrifugation alone) to 91.9% (by blending the two products as discussed above) of fungible bitumen.

EXAMPLE 4

Experiments were conducted to determine the effect on the water content of diluted bitumen products when a mixed solvent is used. In particular, a mixed solvent comprising a naphtha to bitumen (N/B) ratio of 0.5 and an octane to bitumen (O/B) ratio of 1.5 for a total S/B ratio of 2.0 was tested at total solvent to bitumen ratios of 0.7, 1.0 and 2.0 and the water content of the resulting diluted bitumen products determined. Cold octane (unmixed) was also tested at S/B ratios of 0.7, 1.0 and 2.0 to determine the importance of mixing and/or temperature on removal of water/solids from the froth. Mixing and centrifugation were performed as described above in Example 3. Karl Fischer analysis was used to determine the water content. The water content of the diluted bitumen products obtained using mixed solvent and cold octane was compared to the water content in the diluted bitumen products from Example 3 and the results are shown in FIG. 8.

It can be seen from FIG. 8 that comparable diluted bitumen water content was obtained when using pure octane at a O/B ratio of 1.5 and when using mixed solvent having a N/B ratio of 0.5 and octane having a O/B ratio of 1.5 for a total S/B ratio of 2.0. However, the advantage is that the hydrocarbon losses were reduced. Hence, the results suggest that the solvent used in froth treatment can be tailored to achieve the required water content by blending paraffinic solvent and naphtha with the benefit of being closer operation to the 0.5 water+solids limit (for fungible bitumen) and reduced hydrocarbon loss. It was also shown that hot octane with mixing resulted in better water reduction than cold octane, no mixing. Nevertheless, the water content when using cold octane, no mixing, was still reduced to about 0.6 when cold octane was used at a O/B ratio of 2.0.

EXAMPLE 5

In the following experiments, pure octane was added to conventional naphtha bitumen froth treatment in two configurations. FIG. 9 shows Configuration #1 where octane is added to 50% of a naphtha-diluted bitumen froth (e.g., N/B ratio of 0.7) to reach a particular octane to bitumen (O/B) ratio (e.g., 2.0). The naphtha/octane treated froth is then mixed with the other 50% of the naphtha-diiuted bitumen froth, to give a final diluted froth having a total S/B ratio (e.g., 1.75). The final diluted froth is then subjected to centrifugation. FIG. 10 shows Configuration #2 where 50% of naphtha-diluted bitumen froth (e.g., N/B ratio of 0.7) is first centrifuged to give a diluted bitumen product and then octane is added to the diluted bitumen product to reach an particular octane to bitumen (O/B) ratio (e.g., 2.0). The other non-centrifuged 50% of the naphtha-diluted bitumen froth is then mixed with the octane-treated diluted bitumen product to give a mixed product having a total SIB ratio (e.g., 1.64). The mixed product is then subjected to centrifugation.

To test Configuration #1, naphtha, octane and froth were heated inside a hot water bath at 80° C. for 30 minutes. Naphtha was mixed with froth to reach naphtha to bitumen (N/B) ratio of 0.7. Half of the froth mixture was further diluted with octane to reach an octane to bitumen (O/B) ratio of 2.0. The remaining froth mixture (at 0.7N/B) was then recombined with the asphaltene slip stream (2.0 O/B) to form a combined froth mixture containing 1.7 S/B ratio. All streams were mixed inside the water bath at 1000 rpm for 5 minutes prior to and after blending. Two (10 ml) froth mixture samples were taken for each individual froth streams at 0.7 N/B and 2.0 O/B respectively, and three (10 ml) were taken for the combined froth mixture. The (10 ml) froth samples collected at each S/B ratio samples was then subjected to hot spin centrifugation at 80° C. and 1400 rpm for 6 minutes. The top ˜4 ml of the diluted bitumen layer from the centrifuge tubes were drawn from each sample and stored aside for Karl Fischer analysis. Karl Fischer is an analytical test that measures the amount of water content within diluted bitumen sample.

To test Configuration #2, naphtha, octane and froth were heated inside a hot water bath at 80° C. for 30 minutes. Naphtha was mixed with froth to reach naphtha to bitumen (N/B) ratio of 0.7. Half of the froth mixture was centrifuged and the diluted bitumen layer was further diluted with octane to reach an octane to bitumen (O/B) ratio of 2.0. The remaining froth mixture (at 0.7 N/B) was then recombined with the asphaltene slip stream (2.0 O/B) to form a combined froth stream. All streams were mixed inside the water bath at 1000 rpm for 5 minutes prior to and after blending. Two (10 ml) froth mixture samples were taken for each individual froth streams at 0.7 N/B and 2.0 O/B respectively, and three (10 ml) samples were taken for the combined froth mixture. The (10 ml) froth samples collected at each S/B ratio was then subjected to hot spin centrifugation at 80° C. and 1400 rpm for 6 minutes. The top ˜4 ml of the diluted bitumen layer from the centrifuge tubes were drawn from each sample and stored aside for Karl Fischer analysis. Karl Fischer is an analytical test that measures the amount of water content within diluted bitumen sample.

The results shown in FIG. 11 illustrate that there was no benefit in centrifuging the naphtha-diluted bitumen froth prior to the addition of octane (Configuration #2). Thus, only a single centrifuge may be needed when treating naphtha-diluted bitumen froth with paraffin (octane). While the final diluted bitumen product was only of intermediate quality, under the conditions tested herein, it is clear that a better quality product resulted.

From the foregoing description, one skilled in the art can easily ascertain the essential characteristics of this invention, and without departing from the spirit and scope thereof, can make various changes and modifications of the invention to adapt it to various usages and conditions. Thus, the present invention is not intended to be limited to the embodiments shown herein, but is to be accorded the full scope consistent with the claims, wherein reference to an element in the singular, such as by use of the article “a” or “an” is not intended to mean “one and only one” unless specifically so stated, but rather “one or more”. All structural and functional equivalents to the elements of the various embodiments described throughout the disclosure that are known or later come to be known to those of ordinary skill in the art are intended to be encompassed by the elements of the claims. Moreover, nothing disclosed herein is intended to be dedicated to the public regardless of whether such disclosure is explicitly recited in the claims.

REFERENECES

All publications mentioned herein are incorporated herein by reference (where permitted) to disclose and describe the methods and/or materials in connection with which the publications are cited. The publications discussed herein are provided solely for their disclosure prior to the filing date of the present application. Nothing herein is to be construed as an admission that the present invention is not entitled to antedate such publication by virtue of prior invention. Further, the dates of publication provided may be different from the actual publication dates, which may need to be independently confirmed.

Hassan, A.; Hassan, A.; Viswanathan, K.; Borsinger, G. G.; Anthony, R. G. Bitumen extraction and asphaltene removal from heavy crude using high shear. United States Patent Application Publication No. US 2011/0266198, published Nov. 3, 2011.

Tipman, R.; Long, Y.; and Shelfantook, W. E. Solvent process for bitumen separation from oil sands froth. Canadian Patent No. 2,149,737, issued Mar. 2, 1999; U.S. Pat. No. 5,876,592, issued Mar. 2, 1999; Canadian Patent No. 2,217,300, issued Aug. 20, 2002; U.S. Pat. No. 6,214,213, issued Apr. 10, 2001. 

1. A process for cleaning bitumen froth produced from an oil sands extraction process, comprising: a) mixing a sufficient amount of paraffinic solvent with a first portion of the bitumen froth; b) subjecting the resulting first mixture to centrifugal separation in a centrifuge to yield a first diluted bitumen product, a water byproduct stream, and a solids byproduct stream; and c) processing the diluted bitumen product to yield dry fungible bitumen product having a total water/solids content less than about 0.5 wt %, and a recyclable paraffinic diluent stream.
 2. The process of claim 1, wherein the centrifuge is a decanter centrifuge.
 3. The process of claim 1, further comprising processing the water byproduct stream to recover residual bitumen and paraffinic solvent.
 4. The process of claim 3, further comprising processing the solids byproduct stream to prepare a dry granulated powder comprising asphaltenes and fine solids.
 5. The process of claim 4, comprising optionally, mixing a sufficient amount of the asphaltenes with the bitumen froth following addition of the paraffinic solvent in step (a).
 6. The process of claim 5, comprising optionally, subjecting the resulting mixture to mixing in a contactor prior to centrifugal separation in step (b).
 7. The process of claim 1, wherein centrifugal separation is conducted using a three-phrase decanter centrifuge.
 8. The process of claim 7, wherein the diluted bitumen product comprises bitumen, paraffinic solvent, and a water plus solids content that is less than about 0.5 wt %.
 9. The process of claim 8, wherein the diluted bitumen product is transferred from the decanter centrifuge to a diluent recovery unit for recovery of dry bitumen, light gas oil, and paraffinic solvent.
 10. The process of claim 9, wherein the dry bitumen has a total water/solids content less than about 0.5 wt % amenable to processing in a fluid coker or ebullating-bed hydrocracker, or to shipping as fungible bitumen.
 11. The process of claim 1, wherein the water byproduct stream is cleaned in a solvent recovery unit to yield a paraffinic solvent stream for recycling in step (a), and a separate water and fine solids stream for disposal in a tailings pond.
 12. The process of claim 1, wherein the solids byproduct stream comprises asphaltenes, coarse and fine solids, residual paraffinic solvent, and hydrocarbon.
 13. The process of claim 12, wherein the solids byproduct stream is mixed with water and transferred to a flotation cell for separation of an overflow hydrocarbon-rich with fine solids stream and an underflow stream of clean coarse solids.
 14. The process of claim 13, wherein the hydrocarbon-rich with fine solids stream is mixed with paraffinic solvent and spray dried to yield dry granulated powder comprising asphaltenes and fine solids.
 15. The process of claim 14, wherein the powder is mixed with bitumen, heated, and thermally upgraded in a fluid bed or delayed coker.
 16. The process of claim 14, wherein the powder is converted into a syngas in a fluidized bed gasifier or fluid bed boiler.
 17. The process of claim 14, wherein the powder is used as a fuel for a utility boiler or stockpiled as an energy supply.
 18. The process of claim 14, wherein flashed overhead vapour comprising paraffinic solvent and water is condensed in an OVH condenser and decanter to separate the paraffinic solvent from the water.
 19. The process of claim 18, wherein the paraffinic solvent is recycled in step (a).
 20. The process of claim 1, wherein the ratio of paraffinic solvent to raw froth by weight percentage ranges from about 0.5 to about 4.5.
 21. The process of claim 2, wherein the decanter centrifuge is operated to generate a g-force ranging from about 1000 to about
 5000. 22. The process of claim 1, further comprising: d) mixing a sufficient amount of naphthenic solvent with a second portion of the bitumen froth; e) subjecting the resulting second mixture to separation to yield a second diluted bitumen product, a water byproduct stream, and a solids byproduct stream; and f) mixing a portion of the second diluted bitumen product with a portion of the dry fungible bitumen product to produce a final fungible bitumen product.
 23. A process for cleaning bitumen froth produced from an oil sands extraction process, comprising: a) mixing a sufficient amount of naphtha with a first portion of the bitumen froth to produce a first diluted bitumen froth; b) mixing a sufficient amount of paraffinic solvent with the first diluted bitumen froth to form a second diluted bitumen froth; and c) subjecting the second diluted bitumen froth to centrifugal separation in a centrifuge to yield a diluted bitumen product, a water byproduct stream, and a solids byproduct stream.
 24. The process as claimed in claim 23, wherein the diluted bitumen product has a water content of about 1.0 wt % or less. 